Control track pickup



Feb. 16, 1943.4

' J. L. UNDERHILL CONTROL TRACK PICKUP Filed April so, 1941 2 Sheets-Sheet l Snnentr Gttoniei;

Feb. 16, 1943. J. L UNDERHILL CONTROL TRACK PICKUP Filed April 30, 1941 Patented Feb. 16, 1943 UNITED STATES PATENT OFFICE CONTROL TRACK PICKUP Application April 30, 1941, Serial No. 391,085

6 Claims.

This invention relates to control track pickups for picking up the impulses from a sprocket hole type control track in sound film apparatus.

The type of sprocket hole control track which may be used in this apparatus is described in the application of Charles M. Burrill, Serial No. 181,634, filed December 24, 1937, and in Dawson Patent No. 2,199,559. This control track may be used to control the turning on or off of loudspeakers as described in the application of Max C. Batsel, Serial No. 302,197, filed October 31, 1939 (RCV-6981) or it may be used to control the volume of sound reproduced or to otherwise control the amplifying or reproducing apparatus.

The foregoing applications disclose broadly the sprocket hole control track apparatus while the present application pertains tospecific mechanism for the use of such control track film and the reproduction of the control track impulses in a commercial type of sound reproducer.

The apparatus of the present application is described as applied to a sound reproducer of the general type described and claimed in Loomis et al. Patent 2,019,147, issued October 29, 1935.

The invention involves a compact type of reproducer which is peculiarly adapted to the reproduction of the control track and which is so compact that it may be readily added to the soundhead without any material changes there- One object of the invention is to provide a pickup device for reproducing a sprocket hole control track.

Another object of the invention is to provide such a pickup device which may be installed in a commercial soundhead without requiring material modification thereof.

Another object of the invention is to provide such a pickup device which may be installed in a commercial type of soundhead without interfering with the normal operation thereof in the reproduction of sound from the sound record.

Another object of the invention is to provide Such a pickup device which will pick up the impulses from the sprocket hole control track without being materially affected by irregularities in the lateral size or position of the sprocket holes.

Other and incidental objects of the invention will be apparent to those skilled in the art from a reading of the following specification and an inspection of the accompanying drawings in which Figure 1 is a side view of a soundhead including my improved pickup device,

Figure 2 is an enlarged side View partly in section of the pickup device, and

Figure 3 is a vertical section through the pickup device.

Referring first to Fig. l, the casing of the soundhead as described in the Loomis et al. patent referred to above is indicated at I0. The sound reproducing mechanism is supported on the plate II and includes an optical system I2 which directs the scanning beam of light through the film F on the drum I3. Light passed through the sound track of the film is directed through the prismatic lens I4 onto the photocell located in the housing I3. The film is drawn around the drum I3 by the constant speed sprocket IG against which it is held by the pad roller I'I.

In the normal operation of the soundhead the film would pass from between the sprocket I6 and the pad roller I'I to the hold-back sprocket I8 against which it is held by the idler I9 and, there being a free loop of film between the two sprockets the hold-back sprocket would prevent any jerks of the take-up reel from reaching the constant speed sprocket I6. In the present apparatus the loop between the sprockets I6 and I8 is enlarged sufficiently to permit the film to pass over the sprocket hole pickup. This sprocket hole pickup includes a nlm gate 20 which will be described in more detail hereinafter, an exciter lamp 2I housed Within the casing 22 and a photocell housed within the casing 23. The film F is held against the gate 2| by means of the roller 24 and the sprocket I8 which ex over a short span, as indicated in Fig. 1, so as to maintain it in contact with the aperture in the lm gate.

Referring now to the details of the pickup construction as shown in Figs. 2 and 3: The roller 24 which feeds the film into the apparatus is preferably mounted on the common base member 32 which supports both the exciter lamp and the photocell. The exciter lamp 2I is carried in a conventional type of sprocket 28 within the housing 22. The housing 22 is slotted at the bottom portion over the gate 20 to permit the passage of light therethrough and it may be provided with cooling fins 29 and with ventilating apertures 30.

After passing through the aperture in the film gate 20 the light passes through the sprocket hole control track or through the sprocket holes between opaque portions of the track and enters the photocell housing 23 through the aperture 27. The light thereby reaches the photocell 25 which is supported within the housing 23 by the usual socket 26.

The film gate 2G is peculiarly adapted to the present purpose particularly in the construction of the aperture 33 therein. rlhis gate 20 is provided with a base 34 which is aflixed to the base member 32 and which serves to support the gate perpendicularly to the said base member. The face of the gate is relieved so that the picture portion, the sound track portion and the control track portion of the film do not come in contactV therewith.

The sprocket hole type of control track may be affected by diierences in shaping of the sprocket holes in the positive film or by lateral weave of the film and any undesirable effect of these features upon the reproduction' of the track is prevented by the construction of the gate. The aperture in the gate is so constructed as to sharply denne the light beam laterally of the lm and to restrict it to a space slightly narrower than the normal dimensions and positions of the sprocket holes. Longitudinally of the film it is not necessary or desirable to have the edges of the aperture so sharply defined and the aper- .tures correspondingly constructed. In constructing the aperture I prefer to mill out a slot longitudinally of the gate and laterally of the lm, as indicated at 35 in Fig. 3, and which aperture appears in transverse section in Fig. 2. This slot defines the aperture longitudinally of the lm and at the same time it .provides thin edges laterally of the lm for dening the edges of the aperture in that direction. I then cut the aperture through from the opposite or outer side of the gate as indicated at 36 in Fig. 3 which sharply defines the longitudinal sides of the aperture. These longitudinal sides are spaced somewhat more closely together than the rounded ends of the sprocket holes and give correspondingly sharp definition of the track which is reproduced.

The film is pulled over the face of the gate 20 by the hold-back sprocket I8 as this control track does not require the regularity of motion of a conventional sound track. Due to the sprocket hole frequency the normal control frequency is 96 cycles per second and the normal errors in motion of the hold-back sprocket do not materially affect the reproduction of this frequency, while the dimensions of the reproduction aperture prevent the reproduction at any appreciable level of higher frequencies which may be incidental to either sprocket hole irregularities or irregularities in the motion of the sprocket I8.

I claim as my invention:

l. In combination with a soundhead including a photoelectric sound reproducer, a constant speed sprocket for pulling film past the sound reproducer, and a hold back sprocket, a control track reproducer located between the constant speed sprocket and the hold back sprocket whereby the hold back sprocket pulls the film past the control track reproducer.

2. In combination with a soundhead including a photoelectric sound reproducer, a constant speed sprocket for pulling lm past the sound reproducer, and a hold back sprocket, a photoelectric control track reproducer located between the constant speed sprocket and the hold back sprocket whereby the hold back sprocket pulls `the lm past the control track reproducer.

3. In combination with a soundhead including a photoelectric sound reproducer, a constant speed sprocket for pulling lm over a rotatable drum past the sound reproducer, and a hold back sprocket, a control track reproducer located between the constant speed sprocket vand the hold back sprocket whereby the hold back sprocket pulls the film past the control track reproducer.

4. yIn combination with a soundhead including a photoelectric sound reproducer, a constant speed sprocket for pulling lm over a rotatable drum past the sound reproducer, and a hold back sprocket, a photoelectric control track reproducer located between the constant speed sprocket and `the hold back Vsprocket whereby the hold back sprocket pulls the film past the control track 1 reproducer.

5. In combination with a soundhead including a photoelectric sound reproducer, a constant speed sprocket for pulling iilm over a rotatable drum past the sound reproducer, and va hold back sprocket, a photoelectric control track reproducer located between the constant speed sprocket and the hold back sprocket whereby the hold back sprocket pulls the lm past the control track reproducer, said control track reproducer comprising an arcuate lm gate having an Aaperture therein, an exciter lamp located closely adjacent said lm gate, a housing enclosing said -exciter lamp, a photocell adjacent to said aperture and opposite to said exciter lamp, and a housing enclosing said photocell and having an aperture therein facing the film gate aperture whereby said sound reproducer and said control track reproducer each operates without interference from the other.

6. In combination with a photoelectric pickup device for reproducing records from Iilm, an exciter lamp housing adapted to be mounted in a horizontal position for directing light through the lm onto a photocell, said housing including a tubular member having an laperture in one side thereof for transmitting light from the exciter lamp and circumferential cooling ns extending from said housing on the sides away from said aperture.

JOSEPH LEMON UNDERHILL. 

